In order to avoid vibrations during operation in far projecting tools with several cutting edges and with cutting plates of the aforementioned type, a minor cutting edge designed as a guiding edge is provided which is guided along the bore wall. In order to achieve the guiding action, the guiding edge is usually provided with a circular grinding, the radius of curvature of which is smaller than the radius of the bore. This means that the guiding edge is guided along a line on the bore wall. When the circular grinding has a radius which is too small, the guiding becomes relatively poor. The tool chatters because it gets caught on or cuts into the boring wall with the guiding edge. When approaching the bore radius there occurs a surface contact, which increases the friction between the tool and the bore, and which can result in overloads on the machine and/or the tools. The more cutting edges that are arranged over the circumference of the tool, the more serious this effect becomes.
Starting out from this, the basic purpose of the invention is to improve the cutting plates of the above-identified type in such a manner that an optimum support action with a minimum friction results in the area of the minor cutting edge.
To attain this purpose the characteristics disclosed in claim 1 are suggested. Advantageous embodiments and further developments result from the dependent claims.
The inventive solution is based on the thought that a support land is arranged in the area of the minor cutting edge, which support land is defined by two support edges arranged at a distance from each other in the direction of rotation of the tool, which support edges are spaced over their entire length at the same radius distance forming at the same time the flight-circle radius of the tool from the tool axis. Advantageously, the support edges thereby extend in their longitudinal extent parallel to the tool axis, whereas the support land provided between the support edges is designed preferably as a flat surface. The support land advantageously has in its longitudinal extent aligned parallel to the tool axis a length, which length corresponds at least to twice the distance between the support edges. In order to obtain-a minimal friction support, the support edges should be spaced, depending on the bore diameter, at a distance of 0.1 to 1.5 mm from each other. The support land between the support edges thereby advantageously extends over a fraction of the cutting-plate thickness. The support land extends in its longitudinal extent to the, if applicable, rounded or faceted cutting-edge corner. The support edges can be faceted rounded or preferably tangential to the tool flight circle. A preferred embodiment of the invention provides that the major cutting edge and the minor cutting edge designed as a support land define a right angle with each other in their longitudinal extent.
The inventive cutting plate can be designed both as an exchangeable cutting plate with only one cutting-edge corner and also as an indexable insert with several cutting-edge corners. At least two major cutting edges and secondary cutting edges arranged at equal angular distances from each other are provided in the latter case. The cutting plate is advantageously designed as a triangular-like insert with three major cutting edges having a roof shape and a point angle of 140 to 170°, whereby the support land, which is part of a major cutting edge, is formed into the corner area of a major cutting edge adjacent in a defined index direction.
The inventive measures are suited both for use in solid drills and also in core drills and reamers, and thereby are preferably useful in far projecting or long tools with several cutting edges. The tendency of the boring tool to vibrate is reduced by the minimal friction support and guiding in the bore.